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Oxide ceramic matrix composites are currently being developed for aerospace applications such as the exhaust, where the parts are subject to moderately high temperatures (≈ 700 ∘C) and oxidation. These composite materials are normally formed by, among other steps, impregnating a ceramic fabric with a slurry of ceramic particles. This impregnation process can be complex, with voids possibly forming in the fabric depending on the process parameters and material properties. Unwanted voids or macroporosity within the fabric can decrease the mechanical properties of the parts. In order to design an efficient manufacturing process able to impregnate the fabric well, numerical simulations may be used to design the process as well as the slurry. In this context, a tool is created for modeling different processes. Thetis, which solves the Navier-Stokes-Darcy-Brinkman equation using finite volumes, is expanded to take into account capillary pressures on the mesoscale. This formulation allows for more representativity than for Darcy’s law (homogeneous preform) simulations while avoiding the prohibitive simulation times of a full discretization for the composing fibers at the representative elementary volume scale. The resulting tool is first used to investigate the effect of varying the slurry parameters on impregnation evolution. Two different processes, open bath impregnation and wet lay-up, are then studied with emphasis on varying their input parameters (e.g. inlet velocity).

International audience

Nowadays, with the constant evolution of Information Technology (IT) equipments, the energy consumption of data center over the world becomes a major concern. In 2011 the ASHRAE Technical committee 9.9 (TC9.9) issued important guidelines concerning server temperature and hygrometric environment to help engineer in the design of cooling solutions. While raising the temperature may be a source of heat pump energy savings, it induces an increase in the Computer Room Air Handling (CRAH) unit energy requirement, lowering the benefits. Hence optimal temperature cooling set point must be found to maximise the efficiency of the cooling plant. To test various chiller control strategy a “full scale” model is proposed. A 32 kW data center is considered, cooled by a centrifugal heat pump linked to a wet cooling tower. An Integrated Water Side Economizer (IWSE) is added to minimize the energy consumption the regulation and the chilled air production is simulated with the software TRNSYS. The temperature field in the server room is calculated with the CFD code Thetis. To create a link between the 2 simulation environments, a Reduced Order Model (ROM) using Proper Orthogonal Decomposition (POD) is program with MATLAB. Finally this numerical model is used to investigate the effect of server room temperature increase on the cooling plant energy consumption. A new Temperature Adaptive Control Strategy (TACS) that minimizes the energy need is proposed and tested.

Data center electric energy consumption becomes a major issue in HVAC (Heating Ventilating and Air Conditioning) design. In the 2011 guidelines, the ASHRAE (American Society of Heating Refrigerating and Air conditioning engineer) introduces several allowable working envelopes based on temperature and hygrometry. These envelopes encourage the designers to raise cooling air temperature, increasing the COP (Coefficient Of Performance) of the chiller and decreasing its energy consumption. But server's thermal behavior of recent blade server evolves. Their heat rejection is now mainly driven by leakage phenomenon at the CPU level and a FSCA (Fan Speed Control Algorithm) modulate their air flow rate in function of their inside temperature. In this paper we introduce a new way to model this kind of server in a Data center CFD (Computational Fluid Dynamic) code. It includes air speed control with a PID (Proportional Integral Derivative) algorithm, CPU leakage simulation and overall material electric consumption. We will then test this model with different cooling air temperature corresponding to the ASHRAE recommended range. We will try to select the appropriate cooling temperature set point to reach the best compromise between the chiller and the server energy consumption.

This study presents the dynamic behavior of a liquid volume (bridge, film), submitted to different physical phenomena. Effects of surface phenomena such as wetting, surface tension and mechanical phenomena such as strong body force (centrifugation) in various configurations are explored. A numerical modeling approach was undertaken, using Thetis software, developed by I2M (Institute of Mechanics and Engineering of Bordeaux), to study the influence of the mentioned physical phenomena on the displacement of a viscous liquid. At first, in order to illustrate the ability of the numerical model of wettability and to assess its validity, two different test cases are presented. Post-treatment of the results show that static and dynamic contact angles, were satisfactorily simulated. Subsequently, numerical description of the formation of a liquid bridge, due to the growth and coalescence of two microdrops growing at constant flow rate is studied. Then, the evolution of the liquid bridge under the action of a body force is investigated. This case is of practical importance for self-healing matrix composites, whose lifetime depends on the formation and residence time of a viscous plug in micrometric cracks.

In this study, a technique is proposed to improve the filling process of the injection molding and minimize the solidification during the filling to achieve a complete filling of the mold cavity. Two methods are proposed: stopping the flow rate of the cooling fluid or passing cooling fluid inside the cooling channels at higher temperature during a period of the injection molding cycle. The configuration studied consists of the mold with cuboids-shape cavity having two different thicknesses. A validation of the numerical model used by an experimental work is presented. The results show that, stopping of cooling fluid on a period of injection cycle has not great effect on the improvement of injection cycle. The results indicate that passing coolant fluid at higher temperature during the ejection stage decreases the solidification of the polymer during the filling stage by about 40%. © POLYM. ENG. SCI., 2011. © 2011 Society of Plastics Engineers.

Injection molding is one of the most exploited industrial processes in the production of plastic parts. Shrinkage behavior of a molded plastic part plays an important role in determining final dimensions of the part. In this paper, the effect of the cooling system on the shrinkage rate of a polystyrene product during injection molding is carried out. A compressible fluid model for the physical system is presented. A finite volume numerical solution is used for the solution of the physical model. A validation of the numerical model in case of square cavity filled with polymer material is presented. The compressibility behavior of polymer material observed by the pressure, volume, and temperature for the state equation (P–v–T equation) is represented by Tait's equation. A Cross type rheological model depending on the temperature and pressure is assumed for the polymer material. The studied configurations consist of a mold having T-shaped plastic part and four cooling channels. Different cooling channels' positions are assumed and the effect of their positions on the cooling process is studied. The results indicate a good agreement between the numerical solution and those of the literatures. They also, show that the position of the cooling channels has a great effect on final product temperature and the shrinkage rate distribution throughout the product.

Particle transport and heat transfer between particles and ambient fluid are observed in many industrial and natural processes (metal forming, heat storage, etc.). To optimize the manufacturing processes, it is necessary to understand the relationships between global flow, particle transport and heat transfer. The present work deals with the numerical simulation of a cold particle falling (sedimentation) in a hot fluid (of the same material). For a single cold particle in a hot fluid with a low Prandtl number, the results prove that the velocity field is influenced by the thermal behaviour, as natural convection can increase or decrease Archimedes’ forces. The aim is to link the fluid and particles’ properties to the flow and heat transfer to predict occurrence or disappearance of aggregates, numerical methods overcoming limitations previously published.

International audience; No abstract available

The present article reports on the characterization of granular phase changing composites using the T-history method. Further modifications and improvements of the method are employed to handle granular materials undergoing phase change over a temperature range. The accuracy of the T-history method is shown to be limited by the assumption of temperature-independent specific heats and the difficulty of determining the limits of solid and liquid phases. The concept of enthalpy and its relationship with temperature has been employed in the analysis to overcome these difficulties. Enthalpy–temperature and apparent heat capacity curves similar to those obtained using DSC have been developed. These characteristic curves are necessary for accurate design, modeling, and optimization of latent heat thermal energy storage systems. Experiments have been also carried out to measure the transient temperature distribution inside a cylindrical packed bed using phase changing granulates. Analysis of temperature variation along the bed shows good agreement with the measured phase change characteristics. Copyright © 2009 John Wiley & Sons, Ltd.

The present article reports on the feasibility of using encapsulated phase change materials (EPCMs) in the dehumidifying bed of a desiccant cooling system. The mathematical model used to simulate the coupled non-equilibrium heat and moisture transfer processes in the porous composite structure containing the EPCM and desiccant particles is presented. Numerical investigations of heat and mass transfer in a desiccant dehumidifying bed composed of silica gel and EPCM particles have been carried out for different values of process parameters. Careful choices of EPCM volume fraction and thermo physical characteristics have been found to increase the overall effectiveness of the desiccant dehumidifier with negligible loss in the dehumidification efficiency. The air stream exits the desiccant/EPCM bed at relatively lower temperature and slightly higher moisture content than from purely desiccant bed. Desiccant cooling systems with less sensible heating and higher cooling capacity can be obtained by employing EPCM in the dehumidifier.

Impact and solidification of droplets onto a dry solid substrate generates thin or thick substrates depending on size, velocity and physical properties of the fluid particles (during spray or deposition, for example). Numerous and complex phenomena occur in such processes. Difficulties are due to a lack of control of the resulting film, since fluid dynamics (due to droplets impact, for example) heat transfer and solidification interact and influence the final shape and properties of the film. This paper proposes the numerical study of the influence of some material properties upon the manufacturing of a thick coating. For this purpose, a simplified 1D model is used to simulate “deposition” and solidification of successive metal layers upon an initially cold substrate, assuming that there is no fluid flow. Then, the influence of several parameters is studied: layers thickness, initial substrate and layers temperatures, thermal contact resistance between two elements (substrate or layer) and impact frequency.

International audience; Deformations of liquid interfaces by the optical radiation pressure of a focused laser wave were generally expected to display similar behavior, whatever the direction of propagation of the incident beam. Recent experiments showed that the invariance of interface deformations with respect to the direction of propagation of the incident wave is broken at high laser intensities. In the case of a beam propagating from the liquid of smaller refractive index to that of larger one, the interface remains stable, forming a nipple-like shape, while for the opposite direction of propagation, an instability occurs, leading to a long needle-like deformation emitting micro-droplets. While an analytical model successfully predicts the equilibrium shape of weakly deformed interface, very few work has been accomplished in the regime of large interface deformations. In this work, we use the Boundary Integral Element Method (BIEM) to compute the evolution of the shape of a fluid-fluid interface under the effect of a continuous laser wave, and we compare our numerical simulations to experimental data in the regime of large deformations for both upward and downward beam propagation. We confirm the invariance breakdown observed experimentally and find good agreement between predicted and experimental interface hump heights below the instability threshold.

This paper presents numerical experiments inspired by the theoretical work of Faxen for predicting the terminal velocity of a cylinder, settling halfway between two parallel walls at low Reynolds numbers. It is demonstrated that unexpected correlations exist between Faxen's results and the relaxation of a rigid disk initially suspended in a wall-bounded square box. To this end, the 1-Fluid (1F) method is used within a frame of Direct Numerical Simulation (DNS). In first place, the assessment of 1F method in two dimensions is presented. Simulations are in good agreement with Faxen's approach in half-bounded domains, and with simulation data from literature as well. Numerical experiments are then designed in order to investigate the transient behavior of a circular disk in a wall-bounded square box. Significant ranges of particle-to-wall containment ratios, density ratios and Galileo numbers were used in simulations. In the case where the aspect ratio belongs to the range [0.005,0.4] and the Galileo number is smaller than 1, it is found that the wall correction factor based on the maximum settling velocity could be correlated directly with the Faxen's correction factor based on the terminal settling velocity. For extreme values of containment, Faxen's theory gives irrelevant predictions, and alternative approaches based on 1F simulations are suggested. Finally, an original benchmark is designed as an efficient and inexpensive tool for validating numerical approaches to fluid/particle systems.

The present article reports on the research work carried out within the framework of the European project DISTOR. The objective is to conceive, analyze and test systems of storage of thermal energy of the type PCM (phase change materials) adapted to DSG (direct steam generation) technology for electricity production. A detailed model of heat transfer and fluid flow has been reported for numerical simulation of latent heat storage unit which takes into account the solid/liquid and water/vapour phase change processes occurring simultaneously in the PCM and heat transfer fluid with appropriate coupling between them. Reasonable and justified assumptions are then proposed in order to define the most significant process controlling parameters and derive a useful simplified model. Design and optimization procedure have been advised based on the present detailed and simplified models. The influences of various parameters on the operation of the system as well as the potential of new PCM composites are studied.

The present article reports on the fluid flow and heat transfer characteristics associated with cooling an in-line array of discrete protruding heated blocks in a channel by using a single laminar slot air jet. Numerical experiments have been carried out for different values of jet Reynolds number, channel height, slot width, spacing between blocks, block height, and block thermal conductivity. The effects of variation of these parameters are detailed to illustrate important fundamental and practical results that are relevant to the thermal management of electronic packages. In general, the effective cooling of blocks has been observed to increase with the increase of Reynolds number and the decrease of channel height. Heat transfer rates are enhanced for shorter and widely spaced heated blocks. Circulation cells that may appear on the top surface of the downstream blocks have been shown to decrease the value of Nusselt number for these blocks. The values of surface averaged Nusselt number attain their maximum at the block just underneath the impinging air jet, decrease for the downstream blocks, and approximately reach a constant value after the third block. Useful design correlations have been obtained for the mean Nusselt number for the heated blocks underneath and downstream the impinging jet.

Cet article presente une simulation numerique des interactions hydrodynamiques entre une plaque solide en mouvement, un film liquide entraine par cette plaque et un fluide gazeux au repos ou structure en jet plan impactant ce film, dans une hypothese de geometrie cartesienne 2D essentiellement, mais egalement 3D. Cette problematique se rencontre dans des applications procedes "materiaux" (controle d'epaisseur de depot ou d'etats de surface en siderurgie) ou pour dans les parois protectrices (des vehicules spatiaux en phase de rentree atmospherique ou des reacteurs de fusion nucleaire) et d'une certaine facon dans des problemes de condensation avec balayage par un ecoulement gazeux. Ce probleme allie de nombreuses difficultes physiques et numeriques : traitement des interfaces liquide-gaz et des instabilites qui y prennent naissance, turbulence dans la zone gazeuse et eventuellement dans la zone liquide. Une autre difficulte est inherente aux multiples echelles rencontrees : procede a l'echelle centimetrique-metrique, epaisseur de film a l'echelle millimetrique-micronique, echelles de turbulence variees. Notre travail va tenter de vaincre ces difficultes et de produire des resultats en conditions reelles ... ou du moins au plus pres de celles-ci.

The present work deals with heat transfer and fluid flow characteristics during laminar multiple impinging slot jets cooling of a flat plate with symmetrical exhaust ports in the confinement surface. Numerical experiments have been carried out for different values of jet Reynolds number, jet-to-plate separation distance, and exhaust port location. Results have been compared with the base case of single slot jet without cross flow. Reduction in the heat transfer rates induced by spent air removal through the symmetric exhaust ports has been found to be significant for a range of geometrical parameters of practical interest. The introduction of confinement surface protrusions, proposed in the present study, has been shown to be effective in reducing the interaction between jet inlet and exhaust flows and enhancing the heat transfer rates. The corresponding increase in pressure drop is practically not significant. The present results and the effectiveness of the configuration proposed in enhancing heat transfer rates are useful for application to practical devices.

The present article reports on the formulation, numerical implementation, and application of a single-domain coupled micro/macroscopic model for simulation of dendritic alloy solidification. Microscopic solutal non-equilibrium effects have been included in the macroscopic modeling of solidification by using a fixed grid dual scale numerical approach. Salient features of the present approach include a continuum model for conservation of mass, momentum, energy and species on the macroscopic scale, a microscopic solute redistribution model, and the solution procedure and auxiliary equations necessary for coupling between the two models. The coupling between macro and micro scale models is practically made possible by introducing an iterative micro/macro time step scheme. The local solidification rate is calculated by implicit iterations of macroscopic conservation equations and the microscopic solute redistribution model. The present model is capable to simulate eutectic reaction, local re-melting, and account for the inter-linkage between micro and macroscopic solute redistribution (micro and macrosegregation).

PurposeTo study heat transfer kinetics at the fiber scale in order to describe injection of liquid metal through a fibrous perform initially situated in a preheated mould, which is one of the various methods used in order to produce metal matrix composite materials (MMCs).Design/methodology/approachThe first part presents a preliminary study in a static case to describe heat transfer kinetics between a fiber and the matrix in the case of a sudden contact of both components initially set up at different temperatures. This model enables to study the influence of the various parameters of the problem on heat transfer kinetics with phase change. In the second part, we present a modeling which takes into account the metal convection within the pores of the preform.FindingsThe numerical results of these two models justify the instantaneous thermal equilibrium assumption classically admitted to describe MMCs manufacturing methods. The results of this dynamic microscopic model are compared with the results issued from a single temperature macroscopic model to justify the methodological approach and the choice of the microscopic domain geometry representative of the MMCs manufacturing process.Research limitations/implicationsThis first numerical model at the microscopic scale deals with the study of heat transfer between fibers and a pure metal. Next step will be the extension of this study to the preform infiltration by a metal alloy. Injection of matrix alloy implies the appearance of phenomena generated by segregation during phase changes.Originality/valueThe results of simulation tests, making use of the usual conditions of MMCs processing, show pretty good agreement with those of macroscopic models describing the anisothermal flow of a pure metal through a porous medium. From this coherence and from the results of the microscopic models as well, the hypothesis of instantaneous thermal equilibrium between fibers and metal (widely used in the literature to study the production of MMCs by infiltration of the liquid metal through the fibrous reinforcement) is justified. Moreover, it will be possible to extend it to the study of infiltration by an alloy, taking then into account thermal and solutal coupled transfers inside the study domain defined in the present work.

In the present study, two numerical approaches for single-domain modelling of microsegregation during solidification of binary alloys are presented. In the first approach, the concentration jump at the moving solid/liquid interface is formulated using a volumetric term and a Boolean function. The governing solute redistribution equation, valid for the whole domain comprising the solid and liquid regions, is derived in terms of the liquid phase composition. The effects of microstructure coarsening on microsegregation has been described and included in the model. In the second approach, the continuum mixture theory is utilized to derive a single domain solute redistribution equation in terms of the mixture composition. The solidification front motion and dendrite arm coarsening effects are accommodated by considering the representative elementary volume to consist of solid, interdendritic, and extradendritic liquid phases. Numerical solutions have been obtained using a control-volume based finite-difference method with a fixed grid. Good agreement has been observed between the predictions of the present fixed-domain models and the exact analytical and experimental results.

This work is focused on the study of the impingement of a turbulent plane jet on a moving film. A computational fluid dynamics code has been used to simulate the interaction between the turbulent plane jet and the moving film. Since the problem of coupling between turbulence and free surface flow is poorly understood and experiments in this problem are difficult to carry out, this new numerical tool has been designed to give insight into global and local parameters of the free surface flow. To cite this article: D. Lacanette et al., C. R. Mecanique 333 (2005).

The present article reports on a numerical study of heat transfer and fluid flow characteristics during the impact and solidification of liquid droplets on a cold substrate. The impact dynamics and the associated thermal phenomena have been modelled by adopting a fixed grid (Eulerian) approach with a single set of mass, momentum and energy conservation equations. The VOF advection method with TVD front capturing approach has been utilized to track the time dependent droplets location and the interface between the solid, liquid and gas phases within the domain. Numerical experiments have been carried out for both simultaneous and sequential impact of indium liquid droplets on a cold substrate. Findings of the present study are deemed useful for better understanding and control of related surface coating and thin film manufacturing processes. The fluid behaviour and morphology of the resulting thin film have been found to be dependent upon the droplet impact velocity and frequency, and the fluid particles and substrate characteristics.

Numerical experiments have been carried out to investigate natural convection heat transfer and fluid flow characteristics from a horizontal fluid layer with finned bottom surface. The effects of fin height and fin spacing have been investigated for a sufficiently wide range of Rayleigh number. Quantitative comparisons of heat transfer rates and finned surface effectiveness have been reported. The insertion of heat conducting fins has been found to induce an upward fluid motion along the fin walls. For a given value of fin spacing, the number of convection cells between two adjacent fins is function of the values of fin height and Rayleigh number. In comparison with a bare plate, the heat transfer rates for low values of fin height may be decreased by the insertion of fins. For high values of fin height, the finned surface effectiveness is greater than one for a wide range of fin spacing. For low values of Rayleigh number and high values of fin height, the finned surface effectiveness increases linearly with the decrease of fin spacing. Useful guidelines have been suggested to enhance the heat transfer rates from the finned surface.

We have investigated the film thickness and thermal exchange occurring during the coating and cooling of a liquid film on a substrate. The aim of our study is to demonstrate the interest of Direct Numerical Simulation tools for Interfacial flows to understand, on the one hand, the mechanisms involved in the deposition of the film on the moving substrate, and on the other, to measure characteristic parameters of the process. The direct numerical simulation is presented here in two-dimensions based on the Navier-Stokes equations, generalized to free surface flows. They are approximated by VOF (Volume Of Fluid) methods. A Large Eddy Simulation (LES) model is used to take the turbulence into account. We attempt to define the governing parameters of the process and propose a description of the flow. The characteristic parameters of the wiping of the film and the associated thermal exchanges are presented in terms of wiping thickness, transfer coefficient, cooling rate and temperature gradient along the film.

A fixed-domain numerical model for microsegregation during alloy solidification is developed. The phenomena of solute partitioning at the moving solid/liquid interface and subsequent redistribution by diffusion in the solid and liquid phases have been formulated using volumetric terms. A solute balance equation valid for the whole domain comprising the solid and liquid phases has been obtained in terms of the liquid concentration. The effects of microstructure coarsening on microsegregation has been described and included in the present model. Numerical experiments and comparisons have been carried out between the present fixed-domain model, previous deforming-domain models, and the exact analytical solutions available in the literature. Good agreement has been observed between the predictions of the present fixed-domain model and the exact analytical solutions. Further extensions of the present model for the analysis of two-dimensional microsegregation have been also reported.

Numerical simulations on confined bubble trains formed by cross-flowing streams are carried out with the numerical code THETIS which is based on the Volume of Fluid (VOF) method and has been developed for two phase flow studies and especially for a gas-liquid system. The surface tension force, which needs particular attention in order to determine the shape of the interface accurately, is computed using the Continuum Surface Force model (CSF). Through the coupling of a VOF-PLIC technique (Piecewise-Linear Interface Calculation) and a smoothing function of adjustable thickness, the Smooth Volume of Fluid technique (SVOF) is intended to capture accurately strong interface distortion, rupture or reconnection with large density and viscosity contrasts between phases. This approach is extended by using the regular VOF-PLIC technique, while applying a smoothing procedure affecting both physical characteristics averaging and surface tension modeling. The front-capturing strategy is extended to gas injection. We begin by introducing the main physical phenomena occurring during bubble formation in microfluidic systems. Then, an experimental study performed in a cylindrical T-junction for different wetting behaviors is presented. For the wetting configuration, Cartesian 2D numerical simulations concerning the gas-liquid bubble production performed in a T-junction with rectangular, planar cross sections are shown and compared with experimental measurements. Finally, the results obtained of bubble break-up mechanism, shape, transport and pressure drop along the channel will be presented, discussed and compared to some experimental and numerical outcomes given in the literature.

The effects of solid conductive blocks on the initiation of convection in a porous medium are reported in this paper. A two-dimensional convective code was used to determine the temperature field, the structure of the motion, and the global heat transfer through a composite medium consisting of permeable and impermeable areas. Influence of the size of impermeable regions on convection as well as the effect of the distance between these solid blocks was studied in terms of Nusselt number and maximum of the stream function. The predicted heat transfer in this type of composite medium, obtained with the code, was compared with experimental results where the porous medium is a low-density insulating material in which some wood joists are included. This configuration corresponds to the layer of insulation on the floor of a residential attic.

A fixed grid method using an updated iterative implicit scheme is developed to solve one-dimensional phase change problems. The temperature field is deduced from the resolution of the governing equations whose discretization takes into account the discontinuous variation of the temperature derivative at the phase change front. At each iteration an updated position of the moving front is found from the resolution of the energy conservation at the solid-liquid interface. The accuracy of the proposed numerical method has been checked on three test problems.

International audience; During the solidification of metal alloys, chemical heterogeneities at the product scale (macrosegregation) develop. Numerical simulation tools are beginning to appear in the industry, however their predictive capabilities are still limited. We present a numerical benchmark exercise treating the performance of models in the prediction of macrosegregation. In a first stage we defined a "minimal" (i.e. maximally simplified) solidification model, describing the coupling of the solidification of a binary alloy and of the transport phenomena (heat, solute transport and fluid flow) that lead to macrosegregation in a fully columnar ingot with a fixed solid phase. This model is solved by four different numerical codes, employing different numerical methods (FVM and FEM) and various solution schemes. We compare the predictions of the evolution of macrosegregation in a small (10×6 cm) ingot of Sn-10wt%Pb alloys. Further, we present the sensitivities concerning the prediction of instabilities leading to banded channel mesosegregations.

International audience; Recent experimental developments showed that the use of the radiation pressure, induced by a continuous laser wave, to control fluid-fluid interface deformations at the microscale, represents a very promising alternative to electric or magnetic actuation. In this article, we solve numerically the dynamics and steady state of the fluid interface under the effects of buoyancy, capillarity, optical radiation pressure and viscous stress. A precise quantitative validation is shown by comparison with experimental data. New results due to the nonlinear dependence of the optical pressure on the angle of incidence are presented, showing different morphologies of the deformed interface going from needle-like to finger-like shapes, depending on the refractive index contrast. In the transient regime, we show that the viscosity ratio influences the time taken for the deformation to reach steady state.

PurposeThis paper aims to tackle the problem of thermo‐solutal convection and macrosegregation during ingot solidification of metal alloys. Complex flow structures associated with the development of channels segregate and sharp gradients in the solutal field call for the implementation of accurate methods for numerical modeling of alloy solidification. In particular, the solute transport equation is convection dominated and requires special non‐oscillarity type high‐order schemes to handle the regions of channels segregates.Design/methodology/approachIn the present study, a time‐splitting approach has been adopted to separately handle solute advection and diffusion. This splitting technique allows the application of accurate total variation dimensioning (TVD) schemes for solution of solute advection. Applications of second‐order Lax‐Wendroff TVD SUPERBEE and fifth‐order weighted essentially non‐oscillatory (WENO) schemes are described in the present article. Classical numerical solution of solute transport using hybrid and central‐difference schemes are also employed for the purpose of comparisons. Numerical simulations for solidification of Pb‐18%Sn in a two‐dimensional rectangular cavity have been carried out using different numerical schemes.FindingsNumerical results show the difficulty of obtaining grid‐independent solutions with respect to local details in the region of channels. Grid convergence patterns and numerical uncertainty are found to be dependent on the applied scheme. In general, the first‐order hybrid scheme is diffusive and under predicts the formation of channels. The second‐order central‐difference scheme brings about oscillations with possible non‐physical extremes of solute composition in the region of channel segregates due to sharp gradients in the solutal field. The results obtained using TVD and WENO schemes contain no oscillations and show an excellent capture of channels formation and resolution of the interface between solute‐rich and depleted bands. Different stages of channels formation are followed by analyzing thermo‐solutal convection and macrosegregation at different times during solidification.Research limitations/implicationsAccurate prediction of local variation in the solutal and flow fields in the channels regions requires grid refinement up to scales in the order of microscopic dendrite arm spacing. This imposes limitations in terms of large computational time and applicability of available macroscopic models based on classical volume‐averaging techniques.Practical implicationsThe present study is very useful for numerical simulation of macrosegregation during ingot casting of metal alloys.Originality/valueThe paper provides the methodology and application of TVD schemes to predict channel segregates during columnar solidification of metal alloys. It also demonstrates the limitations of classical schemes for simulation of alloy solidification.

Experimental results obtained by guarded hot box testing of low density loose-fill insulations have been analyzed using convective models. Closed and open specimens have been studied in an attic configuration with heat flow up. Experiments were conducted with and without a transverse air flow across the top of the specimens. The occurrence of convective movements inside the insulation was investigated for different applied thermal gradients and air permeabilities of insulation. Comparisons between theoretical and experimental results are presented and discussed. The study has shown that the boundary conditions at the open top surface of an attic insulation are the driving force in determining thermal performance. Both the model and the experiments have shown that a significant reduction in thermal performance for presently used glass fiber insulations can only occur under severe climatic conditions (i.e., where a temperature difference greater than 40°C will be present).

Natural convection in a square cavity in which differentially heated vertical walls are covered with thin porous layers is studied by using a control volume formulation and a SIMPLER algorithm for pressure-velocity coupling. Comparisons with benchmark solutions for natural convection in fluid-filled cavities are first presented for Rayleigh numbers up to 108. The problem of the square cavity with thin porous layers on its vertical walls is then studied by using a modified form of the Navier-Stokes equations by addition of a Darcy term. It is shown that the main effect of the introduction of porous layers is to produce a large decrease of the overall Nusselt number when the permeability is reduced. The higher the Rayleigh number is, the stronger is the decrease, and obviously the decrease also increases with the layer thickness. Moreover, porous layers having a thickness of the order of the boundary layer thickness are sufficient, and taking thicker ones only induces a small decrease of the heat transfer. The main effect of porous layers is to reduce the upwind flow and then to decrease the convective heat transfer.

International audience; We study numerically the deformation of sessile dielectric drops immersed in a second fluid when submitted to the optical radiation pressure of a continuous Gaussian laser wave. Both drop stretching and drop squeezing are investigated at steady state where capillary effects balance the optical radiation pressure. A boundary integral method is implemented to solve the axisymmetric Stokes flow in the two fluids. In the stretching case, we find that the drop shape goes from prolate to near-conical for increasing optical radiation pressure whatever the drop to beam radius ratio and the refractive index contrast between the two fluids. The semi-angle of the cone at equilibrium decreases with the drop to beam radius ratio and is weakly influenced by the index contrast. Above a threshold value of the radiation pressure, these ``optical cones'' become unstable and a disruption is observed. Conversely, when optically squeezed, the drop shifts from an oblate to a concave shape leading to the formation of a stable ``optical torus''. These findings extend the electrohydrodynamics approach of drop deformation to the much less investigated "optical domain" and reveal the openings offered by laser waves to actively manipulate droplets at the micrometer scale.

This paper represents a synthesis of results, both experimental and theoretical, that were obtained from a study of natural convection in fibrous insulat ing materials presenting a permeable interface to the adjacent fluid layer(s)

The purpose of this paper is to simulate numerically the impact of droplets onto a substrate to give a better knowledge of coating manufacturing. A 2D model is proposed, with symmetry conditions to simulate the impact of an infinity of identical droplets. The dynamic behavior is studied, and a thermal study of superimposed splats is added separately to give a better understanding of each phenomenon.Copyright © 2002 by ASME

Abstract Despite many attempts to develop quantitative interpretation methods, the interpretation of temperature profiles has remained mostly qualitative. Most temperature models have concentrated on the wellbore thermal exchanges due to conduction and convection and have assumed that the produced fluid enters the wellbore at the geothermal temperature. Some authors have recognized the importance of the heating or cooling of the produced fluid before it enters the wellbore and have developed models incorporating the Joule-Thomson coefficient to take this into account. Flow in a porous media however does not satisfy the precise definition of a Joule-Thomson is enthalpic process, due to heat transfer between formation and fluid and since the Joule-Thomson process is by definition steady state both in terms of pressure and temperature. This paper describes an energy equation that takes into account the temperature effects due to the decompression of the fluid and the frictional heating that occurs in the formation, and how this equation is coupled with the pressure equations in a finite element numerical well model. The application to temperature log interpretation is demonstrated on real data sets. The ultimate goal would be to use the thermometry model for multilayer interpretations that differs from conventional methods in that both rate temperature can be matched. Introduction A recent publication has presented a new model for determining the temperature of flow in porous media. This model, MOTHER (Modelling THERmometry), has the particularity to solve a new energy equation. A short reminder will first present the structure of MOTHER. The main objective in measuring temperature in a flowing well is to locate flowing anomalies and eventually to track the fluid inside (and/or outside) the tubing. In that purpose, the main type curves have been calculated, emphasizing multi- layer oil/gas production and reproducing anomalic fluid behaviour such as upward and downward channeling. Cross flow (partial or integral) and fluid injection (to some extents) can also be simulated. MOTHER becomes then a qualitative tool for interpreting temperature measurements. However, the second part of the present paper, developing a real case, will show that the intensity of the thermal effects are not yet completely reproduced. The purpose of this paper is to discuss the reasons of this temperature misfit by quantifying the main thermal effect appearing under stationary and adiabatic conditions: the Joule-Thomson effect. P. 247^

International audience; It is currently debated if either thermal erosion of the lithosphere or dynamical support is the source of topography and geoid anomalies. The origin of this controversy lies probably in the difficulty to model simultaneously these two effects. For this purpose we have studied the time dependent behavior of two-dimensional convection with a temperature and pressure dependent viscosity. The use of a control volume method allows us to define a rigid zone simulating the mechanical lithosphere. The interface between the lithosphere and the convective mantle is determined by a viscosity cutoff. First, some experiments model the rise of a plume below the lithosphere in order to observe the evolution of the uplift and thus to appreciate the various processes involved in the swell formation. Before the plume reaches the base of the thermal lithosphere, an uplift a few hundred meters in amplitude develops which can only be ascribed to a pure dynamical support. The major uplift occurs when the ductile part of the lithosphere, the convective boundary layer, is squeezed by the plume. The reheating of the mechanical lithosphere takes place after this transient stage of dynamical erosion. However, this late process is very slow but can magnify the amplitude of the swell if the lithosphere stays long enough above the plume. These results shed some light on the different mechanisms occurring during the swell formation, but the configuration modeled does not correspond to the one expected for actual hotspot swells. They feature plume rising up to the lithosphere while natural situations correspond to lithosphere drifting above preexisting plumes. An experiment with a moving lithosphere was run and shows that thermal erosion does not affect significantly a moving lithosphere even for relatively slow drifting velocities (few centimeters/year). Indeed, the thermal structure of the lithosphere is not modified above the 800øC isotherm except for a motionless plate. In this case the resulting swell should be greater: this could explain why Azores, Crozet or Cap Verde swells are so high. On the other hand, the shape of a swell over a moving lithosphere is strikingly reminiscent of the Hawaiian swell.

Coating techniques are frequently used in industrial processes such as paper manufacturing, wire sleeving, and in the iron and steel industry. Depending on the application considered, the thickness of the resulting substrate is controlled by mechanical (scraper), electromagnetic (if the entrained fluid is appropriated), or hydrodynamic (gas-jet wiping) operations. This paper deals with the latter process, referred to as gas-jet wiping, in which a turbulent slot jet is used to wipe the coating film dragged by a moving substrate. This mechanism relies on the gas-jet–liquid film interaction taking place on the moving surface. The aim of this study is to compare the results obtained by a lubrication one–dimensional model, numerical volume of fluid–large eddy simulation (VOF-LES) modeling and an experimental approach. The investigation emphasizes the effect of the controlling wiping parameters, i.e., the pressure gradient and shear stress distributions induced by the jet, on the shape of the liquid film. Those...